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Participant

Join Date: Nov 2008
Posts: 2

Optical Encoders and Laser Interferometers

11/06/2008 8:52 AM

How does an optical encoder differ from a laser interferometer?

I need to make a non contact measurement of minute positional change.

What is the price range and or is it possible to lease one and for what kind of price?

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Guru

Join Date: Sep 2007
Location: Defreestville, NY
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#1

Re: what IS an optical encoder?

11/06/2008 9:25 AM

How minute is your positional change ? Is it angular or linear?

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#2
In reply to #1

Re: what IS an optical encoder?

11/06/2008 9:49 AM

Hello stevem,

I plan to measure the motion of a torsion pendulum. I expect the range to be microns or less. So it is both linear and rotational.

Thanks for replying. jim

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#3
In reply to #2

Re: what IS an optical encoder?

11/06/2008 10:38 AM

Encoder background : http://en.wikipedia.org/wiki/Rotary_encoder

Since your application needs to non-contact you may want to consider using a magnetic encoder or a resolver.

http://www.admotec.com/magnetic_encoders.htm

http://en.wikipedia.org/wiki/Resolver_(electrical)

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Guru

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#4

Re: what IS an optical encoder?

11/06/2008 12:42 PM

Any encoder disk whichever design will have an inertia so that if you measure a torsion this inertia will add and may be change the natural frequency. You could use a distance measurement using a triangulation principle which is based on a reflected IR light.The surface of your rotating part has to be reflective.

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Guru

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#5
In reply to #4

Re: what IS an optical encoder?

11/06/2008 1:54 PM

True, in that case either a capacitive or fiberoptic probe could be used.

http://www.mtiinstruments.com/products/mti2100fotonic.aspx

Before anything can be suggested we will need to know the range, precision and response time required of the application.

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#6

Re: Optical Encoders and Laser Interferometers

11/07/2008 2:19 AM

Hi,

very good and very sensitive capacitive transducers are made by

Lion-Precision (St.Paul)

Fogale-Nanotech (France)

Micro-Epsilon (Germany)

PI (Germany)

I tested these and had very good results.

Then I made my own ones - much cheaper.

Laser triangulation is not at all near the quality of capacitive sensing for small distances.

RHABE

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Anonymous Poster
#7

Re: Optical Encoders and Laser Interferometers

11/07/2008 12:15 PM

Call Keyance. They have systems directly designed for this application. I have one that we measure dynamic movement of piezoelectric transducers during actuation in the 0.05 to 25 um @ up to 150 Hz.

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Anonymous Poster (1); bluelakecabin123 (1); nick name (1); RHABE (1); stevem (3)

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